| Author |
Message |
    
beatlejuice
| | Posted on Monday, February 17, 2003 - 5:34 am: | 
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need info on how to put varible power in a d&a raider amp so i can lower my dead key down to about 10w -15w dead key |
poor raider
| | Posted on Tuesday, February 18, 2003 - 2:15 am: |
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try tunning the tune and load controls! and leave varible power to the 10 meter radios and texas star mobile amps.
why on earth do you want to do this to your amp? |
Beatlejuice
| | Posted on Tuesday, February 18, 2003 - 4:16 am: |
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im useing it to to drive my heathkit sb 220 it keys about 30 and swing 120 but with my heath it makes it key about about 300w and swing to 1400+watts if i can get the deadkey down to 10 to 15 my heath would only key about 100w and swing to 1400+ that would make it better on all the tubes . |
2600
| | Posted on Wednesday, February 19, 2003 - 10:56 pm: |
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Hey Beatlejuice,
Sounds like you have a radio with a FIXED dead key with NO variable power knob. This leaves you with no other choice than to use the driver for this purpose. People have used the Black Cat "JB" series small modulator amplifiers to do this for years. The "Jewel Box" amplfiers are designed to control the carrier level from the very start. They were designed 30 years ago when a radio with "variable key" was just a pipe dream. Some clever fella at Wawasee Electronics figured out a way to reduce the carrier in a tube amplifier WITHOUT reducing the modulated swing. You set the little chrome knob in the back to the desired carrier power.
So far, so good. Your D&A Raider is built a little differently on the inside. One major thing you are missing is a source of NEGATIVE polarity power at 70 to 90 Volts DC. The Raider doesn't provide you an easy way to come up with it. This means adding a small transformer inside to step the line-cord voltage down to about 60 Volts, a rectifier and a filter to go onto it.
This negative-hot (positive grounded) BIAS voltage then gets fed (through the variable key control) to two pins on each tube socket. Problem is, those eight tube-socket pins are now soldered to GROUND, and will often snap off from the socket as you unsolder them from ground.
From this point in the process, it starts to get complicated.
So just how big a deal is it to use a radio that has variable key? On the whole, might that prove to be cheaper than rewiring the Raider to add grid bias?
Bear in mind that those two pins per socket that are grounded in the Raider create another "gotcha" if you DO use a radio with variable key. The "zero bias" hookup on those four tubes will often cause them to overheat if you use it either on SSB (no carrier at all) OR with you AM carrier turned TOO LOW. The Raider was designed when there was no such thing as a "variable key" radio, and isn't designed to tolerate that well. If your tubes behave and don't "cherry", or overheat enough to glow red, with 1 Watt carrier from the radio that's fine, but a lot of them will. The cure for that? Popping those eight tube socket pins loose from ground and installing fixed (not variable) bias voltage onto the four tubes.
Either way, whether you put a radio with variable key on this station or not, some kind of bias will probably have to get added to the Raider to keep it happy.
If you really are interested in doing such "invasive" surgery on the Raider, speak up. The BIll of Materials for this trick is pretty long all by itself. Then again, a different combination of radio/driver might start sounding better by now.
73 |
bullet
| | Posted on Saturday, February 22, 2003 - 12:55 am: |
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read your heathkit manual and look up the specs on the 3-500z tubes.
after doing so set up the amp within thier paramiters for the tubes and youll see it keying around 400watts carrier swinging to around 1300+ and will do this for 20+ years on those same tubes,as long as you dont drive/load the hell out of it. |
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